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<h2><span class="refentrytitle">Struct template constructible_with_allocator_prefix</span></h2>
<p>boost::container::constructible_with_allocator_prefix</p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../boost_container_header_reference.html#header.boost.container.scoped_allocator_hpp" title="Header &lt;boost/container/scoped_allocator.hpp&gt;">boost/container/scoped_allocator.hpp</a>&gt;

</span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> T<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="constructible__idp14760432.html" title="Struct template constructible_with_allocator_prefix">constructible_with_allocator_prefix</a> <span class="special">{</span>
<span class="special">}</span><span class="special">;</span></pre></div>
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<a name="idp39048032"></a><h2>Description</h2>
<p><span class="bold"><strong>Remark</strong></span>: if a specialization is derived from true_type, indicates that T may be constructed with allocator_arg and T::allocator_type as its first two constructor arguments. Ideally, all constructors of T (including the copy and move constructors) should have a variant that accepts these two initial arguments.</p>
<p><span class="bold"><strong>Requires</strong></span>: if a specialization is derived from true_type, T must have a nested type, allocator_type and at least one constructor for which <a class="link" href="allocator_arg_t.html" title="Struct allocator_arg_t">allocator_arg_t</a> is the first parameter and allocator_type is the second parameter. If not all constructors of T can be called with these initial arguments, and if T is used in a context where a container must call such a constructor, then the program is ill-formed.</p>
<p>[Example: template &lt;class T, class Allocator = allocator&lt;T&gt; &gt; class Y { public: typedef Allocator allocator_type;</p>
<p>Default constructor with and allocator-extended default constructor Y(); Y(allocator_arg_t, const allocator_type&amp; a);</p>
<p>Copy constructor and allocator-extended copy constructor Y(const Y&amp; yy); Y(allocator_arg_t, const allocator_type&amp; a, const Y&amp; yy);</p>
<p>Variadic constructor and allocator-extended variadic constructor template&lt;class ...Args&gt; Y(Args&amp;&amp; args...); template&lt;class ...Args&gt; Y(<a class="link" href="allocator_arg_t.html" title="Struct allocator_arg_t">allocator_arg_t</a>, const allocator_type&amp; a, Args&amp;&amp;... args); };</p>
<p>Specialize trait for class template Y template &lt;class T, class Allocator = allocator&lt;T&gt; &gt; struct <a class="link" href="constructible__idp14760432.html" title="Struct template constructible_with_allocator_prefix">constructible_with_allocator_prefix</a>&lt;Y&lt;T,Allocator&gt; &gt; : ::boost::true_type { };</p>
<p>-- end example]</p>
<p><span class="bold"><strong>Note</strong></span>: This trait is a workaround inspired by "N2554: The Scoped Allocator Model (Rev 2)" (Pablo Halpern, 2008-02-29) to backport the scoped allocator model to C++03, as in C++03 there is no mechanism to detect if a type can be constructed from arbitrary arguments. Applications aiming portability with several compilers should always define this trait.</p>
<p>In conforming C++11 compilers or compilers supporting SFINAE expressions (when BOOST_NO_SFINAE_EXPR is NOT defined), this trait is ignored and C++11 rules will be used to detect if a type should be constructed with suffix or prefix allocator arguments. </p>
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